1. Field of the Invention
This invention relates to a method and apparatus for tire condition assessment which is particularly but not exclusively applicable to automotive vehicles. An example of the application of the invention is a method and apparatus which could be incorporated into automotive wheel balance or brake testing equipment so that a simultaneous or contemporaneous assessment of tire tread and sidewall and other tire condition factors may be made when other wheel tests are performed on a vehicle. Likewise, the invention is also applicable to test equipment in the form, for example, comprising a drive-on ramp applicable to road side testing of a vehicle tire in situ, without dismounting from a vehicle. Such applications of the invention would be suitable for law enforcement and regulation compliance authorities and their mobile personnel. A further application relates to test equipment used by commercial roadside test operations, particularly those specializing in rapid test services.
2. Description of the Prior Art
Known systems in relation to tire tread assessment include the usual manual measurement techniques including the use of tread depth gauges for insertion into the tread, and the assessment of tread wear by image analysis of a track after paint-treatment of the tread.
Such prior systems are relatively crude and inconvenient to use in an automotive industry which requires relatively instantaneous assessment of vehicle equipment and operational characteristics.
There is disclosed in International publication number WO96/10727 (Russell) tire scanning apparatus and a corresponding method which is able to provide an output indicative of information relating to tire tread depth. In an embodiment, a laser sensor is utilized in relation to a tire which is rotated while the laser sensor is mechanically scanned across the lateral width of the tire tread, being carried on a carriage which can reciprocate across the tire width on slide rods or bars. By virtue of the lateral motion of the carriage, the single laser point is mechanically scanned across the tire. Such an arrangement is subject to significant shortcomings in terms of the ability of the apparatus to provide an acceptable range of tread determinations on a given wheel within the short period of time available for a roadside test. The system inevitably is subject to the mechanical limitations of the scanning mechanism for the laser point source, whereby the time implications of a complete scanning operation for a single wheel become unacceptable, and some means is needed to enable a substantially greater rate of tread assessment in order to provide a realistic and practical form of apparatus.
There is disclosed in DE 4316984 A1 (Mercedes) a system for automatic measurement of tire profile in which the profile is measured along a line across the rolling direction of the tire by a traversing measuring head using a contactless optical triangulation method. This system is likewise subject to the performance shortcomings of the previously described reference.
There is disclosed in GB 2 241 061A (FMC) a structured light scanning system for use in automotive service equipment in which a laser source directs a beam of known shape onto a wheel rim/tire assembly so as to form a light stripe thereon. As described on pages 9 and 10, the stripe 22 of light impinges the tire/rim assembly 21/19 and an array of sensing cells are excited. Pixels 52b are raised with respect to their neighbors and correspond to the valve stem 27 on the rim. Pixels 53b on the sensing cells correspond to the bump in the light stripe 22 where it intersects the periphery of the rim 19 of the wheel. The system is particularly applicable to determination of tire/rim assembly balance, runout and alignment or brake surface planarity and smoothness determinations.